Bug 13205: [FOLLOW-UP] Fixing math and variable names

Bug 13205: [FOLLOW-UP] Fixing math and variable names

Have changed
  my $last_page = $pages * ( $results_per_page - 1 );
to
  my $last_page = ( $pages - 1) * $results_per_page;
which seems to fix the 'last' button offset! (Comment 10)

Will add the box to jump to a page in a separate patch.
Adding the pagination to the top on the staff client will be dealt with
in Bug 18916 as it is slightly out of the scope of this bug.

Signed-off-by: Lee Jamison <ldjamison@marywood.edu>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>